Here's the California House race that could crush Democrats' hopes in the 2018 midterms

• The balance of power in the House – and perhaps the fate of the Trump presidency – may come down to one predominantly Latino district in central California.
• The son of a Latino labor rights icon Delores Huerta who was trounced in 2016 is back challenging the GOP incumbent for the seat in California's 21st District
• Democrats worry that they may not be fielding the best candidate in a district where Clinton beat Trump by 15 points in 2016, but their hands appear to be tied.

Huerta For Congress Campaign | AP

Emilio Huerta , son of UFW co–founder Dolores Huerta is running in the 21st District of the State of California.

There are countless hashtags floating around the internet that reflect liberals' optimism that Democrats will be able to retake the House of Representatives in 2018: #Bluewave2018, #BlueTsunami, #FlipTheHouse.

In my extensive travels across the country the past few months – particularly to districts that are deemed "toss-up" seats by Washington soothsayers – I have been struck by how much Democratic voters seem to be zeroed in on what they will do once their party regains control of the House: Sunset the Expiring Provisions of the Patriot Act. Roll Back ACHA! Impeach Trump!!

Hashtags notwithstanding, before progressives can put the pedal to the metal on their congressional agenda, they need to understand that the math that puts Democrats back behind the wheel of the House is tricky. And they need to start paying attention to one California congressional race in particular that has been largely off the national radar.

As it stands, the Democratic effort to retake control of the House of Representatives hinges upon the outcomes of just a handful races. At present, Democrats control 193 seats to the Republicans' 238, and there are four vacant seats. This means Democrats will have to pick up 24 seats to hold a one vote majority – 218 vs 217, assuming there are no vacancies.

The Cook Political Report – the bible of beltway odds-making – has earmarked seven GOP-controlled seats as "Likely Democratic" or "Lean Democratic," and lists another 19 GOP-controlled seats as "Toss Up."

Of course, if Democrats were to run the tables and pick up every Toss Up seat in play, they would certainly be in a position to retake the House. But running the tables is not a surefire game plan - it's wishful thinking at best.

The far more likely scenario is that Democrats will able to pick up those GOP-held "Toss Up" and "Lean Republican" seats that broke for Hillary Clinton in 2016. The thinking is that if a district went for Clinton at the top of the ticket yet voted in Republicans down ballot, the dynamic was about providing a check on what voters saw as the likely election of Clinton.

The unexpected election of Trump, and the deluge of near-daily debacles that have come to define the first year of his Administration, have in all likelihood made most of these pro-Clinton "Toss Up" and "Lean Republican" seats winnable for Democrats.

There are 16 Cook Toss Up and Lean Republican seats that went for Clinton, yet even if Democrats bat a perfect 1.000 in these races and win everywhere else they are supposed to win, they will still be one seat short of a majority. To take control of the House, Democrats will have to flip at least one seat that Cook and others have deemed Likely Republican.

And that brings us back to California – Fresno, to be specific.

California's 21st congressional seat is one of two "Likely Republican" seats that broke for Clinton in 2016. (The other is New York's 24th district, where there doesn't appear to be a strong challenger to GOP incumbent John Katko.)

The showdown in Fresno will be a rematch of 2016, in which GOP incumbent David Valadao handily beat first-time candidate Emilio Huerta, winning 56 percent of the vote, even though Clinton trounced Trump by more than 15 points in the district.

Huerta is the son of Latino civil rights icon Dolores Huerta, which should have given him a strong following in a district that trends Democratic and is over 70 percent Hispanic; yet, astonishingly, the Democratic Congressional Campaign Committee has been somewhat reluctant to get engaged in the race because, as the Los Angeles Times has reported, some party officials in Washington feel that they have been strong-armed into supporting Huerta by his influential mother.

The allegations suggest that the elder Huerta, whom Obama bestowed with a Presidential Medal of Honor, has consistently shot down any talk of other potential candidates mulling a primary challenge to her son.

The California Democratic primary is scheduled for June, but in last month's byzantine "pre-endorsement conferences" – the process that winnows down the candidate pool for official party endorsements ahead of the primary –Huerta emerged as the lone congressional candidate statewide who slipped through unchallenged. (By contrast, the average California Democratic primary has half a dozen candidates vying for the right to unseat the incumbent Republican.)

Democrats in the district accuse Dolores Huerta, who remains a force in California politics by making coveted endorsements and frequent campaign appearances, of threatening to pull any future support from anyone challenging her son in the district's primary; it is indeed difficult to imagine any Latino Democrat winning a race anywhere in Central California without the full-throated endorsement of the woman who made her name organizing Latino farm laborers in the 1960s alongside César Chavez.

The race in California's 21st – a sleeper contest that hasn't yet attracted much national media nor out-of-state donor interest – may very well prove to be the linchpin that decides if the House rolls Democratic or Republican this fall.

With the die all but cast on the party's choice to go up against Valadao in November, now the DCCC has no option but to get on board and encourage the national donor base to focus more resources on propping up their party's candidate in California's 21st. (Valadao raised 10 times as much as Huerta last quarter.)

One immediate step that could be taken is to add Huerta to DCCC's "Red to Blue" program, which serves as a cheat-sheet for where national party donors should direct their cash.

If Democrats fail to flip the seat and find themselves one vote short of a majority, many in the party will inevitably cast blame on an iconic labor leader and her protective maternal instincts for meddling in a race might have been won with a different candidate on the ballot. But the real blame will fall at the feet of the DCCC for failing to embrace Huerta, and giving him the resources he needed to win a very winnable seat.

Commentary by Arick Wierson, a six-time Emmy Award-winning television executive and former deputy commissioner under New York City Mayor Michael Bloomberg. Currently, Wierson works as a political and branding consultant to clients in the United States, Africa and Latin America. He is currently advising candidates in U.S. House races in Southern California, Michigan, Minnesota and Wisconsin as well as several state gubernatorial candidates in Brazil. He is not affiliated with the race in California's 21st District. You can follow him on twitter @ArickWierson.

For more insight from CNBC contributors, follow @CNBCopinion on Twitter.

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